This invention relates in general to the heat-treating of metal and in particular to the heating of metal stock in the form of slabs, sheets, or strips.
A great deal of thought and effort has gone into the development and improvement of efficiency of heat-treating apparatus. The increasing cost of energy has given new impetus to such development, particularly in the field of heat-treatment of metal.
In the case of flat metal stock, for example, continuous treatment of moving lengths of stock is conventional. Generally, the stock to be treated is continuously advanced through a furnace where it is heated radiantly or by convection. In fact, there have been some heat-treating systems where radiation and convection have been used simultaneously to increase the efficiency of heat transfer.
One such system is described in U.S. Pat. No. 4,202,661, entitled "Jet Impingement Radiation Furnace, Method and Apparatus", which issued May 14, 1980 to Thermo Electron Corporation. In this system, strip stock is advanced continuously through a furnace on rollers beneath a perforated refractory plate which is heated to radiance and through which jets of combustion are directed upon the upper surface of the strip stock.
Although the patented system achieved a considerable improvement over systems then in use in efficiency of heating stock by utilizing both radiant and convective heating, the furnace was somewhat cumbersome and involved complex structural elements. For example, the perforated plates and the combustion chambers employed therein presented problems with maintaining acceptable seals and with developing the high pressures and velocities needed for large amounts of convection heat transfer. Moreover, structural complexities limited the system to heating stock only from a single side thereof.
Accordingly, a primary object of the present invention is to improve further the efficiency of combined radiant and convective heating of flat metal stock by simplifying design and reducing the size of the furnace without losing heating productivity.
A further object of the present invention is to heat-treat both sides of flat metal stock continuously with direct convective and direct radiant heating.
Another object of the present invention is to minimize oxidation by rapidly raising the temperature of the material being processed and by utilizing secondary heat transfer to reduce the temperature of flue gases.
Still another object is to reduce the cost of heat-treating materials.